1. Field of the Invention
The present invention relates to photon detection systems and, more particularly, to correcting the pulse counts output by multi-pixel photon counting detectors of such systems.
2. Description of Related Art
Applications that utilize gamma or x-ray cameras, gages or imaging systems based on pixilated semiconducting radiation detectors require the use of measured counts per pixel in a given period of time to accurately discern the incident photon flux density. Most imaging applications rely on a collective uniform response of the pixels of the system when subjected to a uniform incident photon flux density. However, the material upon which such systems are based has crystal defect densities that are spatially non-uniform, thereby producing a non-uniform pixel response (sensitivity). At high flux densities, the non-uniform pixel response due to material sensitivity is made worse by a non-linear loss in measured counts due to the response of readout electronics.
For example, a typical response of a 64 pixel CdZnTe detector subjected to increasing flux density is shown in the accompanying FIG. 4. Non-uniform pixel sensitivity coupled with the effect of the readout electronics can be seen by an increasing spread of the high and low counting pixels for a given flux density, typically expressed in terms of x-ray tube current.
If the dependence of photon flux density (expressed in terms of x-ray tube current) in FIG. 4 to a number of counts output by each pixel were linear, it would be trivial to correct the counts across the desired photon flux density. Namely, simply elevate (or suppress) a pixel's counts to some averaged level using a constant multiplier. FIG. 4, however, demonstrates that for higher fluxes this dependence is, in fact, quite nonlinear. A single-point sensitivity correction then becomes dependent on the flux density at which the correction is being done. One solution is to break the desired flux density range into multiple intervals, and on each sub-interval apply a single point correction. These correction schemes all operate solely on measured counts. However, these correction schemes fail away from the flux density where the correction was made.
It would, therefore, be desirable to provide a method and system for correcting the pulse counts output by pixels of a photon detection system that avoids the above problems and others. Still other problems that the present invention overcomes will become apparent to those of ordinary skill in the art upon reading and understanding the following detailed description.